When an underground pipe, such as a pipeline and a passageway, becomes defective or too old to perform properly, the pipe is repaired and rehabilitated without digging the earth to expose the pipe and disassembling the sections of the pipe. This non-digging method of repairing an underground pipe has been known and practiced commonly in the field of civil engineering. Typically, the method is disclosed by Japanese Provisional Patent Publication (Kokai) No. 60-242038.
According to this publication, this method of pipe repair comprises inserting a sufficiently long tubular flexible liner bag into the pipe to be repaired by means of a pressurized fluid, like air and water. The tubular liner bag is made of a flexible resin-absorbent material impregnated with a thermosetting resin, and has the outer surface covered with an impermeable plastic film.
More particularly, according to the publication, the tubular flexible liner bag is closed at one end and open at the other; the tubular flexible liner bag is first flattened, then, the closed end of the tubular liner bag is tied to a control rope; the open end of the tubular liner bag is made to gape wide and hooked (anchored) at the end of the defective or old pipe in a manner such that the wide-opened end of the liner completely and fixedly covers and closes the pipe end; a portion of the liner is pushed into the pipe; then, the pressurized fluid is applied to the said portion of the tubular liner such that the fluid urges the tubular liner to enter the pipe. Since one end of the tubular liner is hooked at the end of the pipe, it remains there while the rest of the flexible liner bag is turned inside out as it proceeds deeper in the pipe. (Hereinafter, this manner of insertion shall be called "everting".) When the entire length of the tubular liner bag is everted(i.e., turned inside out) into the pipe, the control rope holds the closed end of the tubular liner bag to thereby control the length of the tubular liner in the pipe. Then, the everted tubular liner is pressed against the inner wall of the pipe by the said pressurized fluid, and the tubular flexible liner is hardened as the thermosetting resin impregnated in the liner is heated, which is effected by heating the fluid filling the tubular liner bag by means of a hot steam, etc. It is thus possible to line the inside wall of the defective or old pipe with a rigid liner without digging the ground and disassembling the pipe sections.
When, however, this method is applied to a pipe having a second pipe branching out from it, like the one 123 shown by cross section in FIG. 10, it is necessary to cut off that portion of the liner 125 which closes the branch pipe 124.
To do so, an on-the-sleigh robot (cutter apparatus), like the one 101 shown in FIG. 11, having a hole saw type rotary grinder disk 116 of a diameter corresponding to the size of the branch pipe 124 is conventionally employed, which is brought in the main pipe 123 and operated to cut and remove that portion of the the liner 125 which closes the opening of the branch pipe 124, so as to establish communication between the main pipe 123 and the branch pipe 124. As shown, the rotary grinder disk 116 is topped with a conical grinding cutter.
The on-the-sleigh robot 101 as described above comprises a robot main body 106, which is mounted on a pair of sleigh boards and thus capable of sliding to move in the main pipe. On the robot main body 106 are mounted a flash light 107 and a TV camera 108 for monitoring. Further, a vertical piston cylinder 112 having a piston rod is connected to the head of the robot main body 106, and a motor 115 is supported on the piston rod in a manner such that the motor 115 can be shifted up and down, and the rotary grinder disk 116 is locked about the end of the output shaft of the motor 115.
Thus, in an operation of removing that round portion of the liner 125 which closes the branch pipe, the on-the-sleigh robot 101 is first introduced into the main pipe 123 and brought to the optimum position, as shown in FIG. 11, and then the motor 115 is started and the piston cylinder 112 is operated to raise the turning grinder disk 116 toward the liner 125. Thus, the obstacle portion of the liner 125 is ground off by the grinder disk 116, and the communication between the main pipe 123 and the branch pipe 124 is resumed.
Now, in the conventional on-the-sleigh robot 101 shown in FIG. 11, the maximum distance through which the grinder disk 116 can move vertically is limited by the stroke length through which the piston cylinder 112 can reciprocate its piston rod, so that depending on the diameter of the main pipe 123, it can happen that the grinder disk 116 fails to completely grind off the obstacle portion of the liner 125. As shown in FIG. 10, the smaller the radius r (D/2) of the main pipe 123 is (that is, the greater the curvature is), the greater will the warpage height H of the obstacle portion of the liner 125 be; so that in the case of a pipe of a relatively small diameter, this problem is more liable to occur.